Compounds from the elderberry fruit block the flu virus from spreading and replicating and also strengthen the immune system's response to the virus.
As such, it's more effective than the seasonal flu jab that, at best, has a 40 per cent success rate.
Researchers at the University of Sydney in Australia extracted juice from elderberries they bought from a farm and applied them to cells in the laboratory before, during and after they had been infected with the influenza virus.
The phytochemicals from the juice stopped the virus infecting the cells and also blocked the virus propagating at later stages in the process and after the cells had been infected.
It also stimulated the cells to release cytokines, chemical messengers that help the immune system communicate between different cell types.
The black elderberry (sambucus nigra) is an antioxidant-rich fruit, and its extract is commercially available as a tablet or syrup.
The flu virus kills about one million people a year around the world.